Ratfor is preprocessor for FORTRAN code that allows us to use C-like flow expressions. Jon Claerbout believes that Ratfor is the best available expository language for mathematical algorithms. Ratfor was invented by Brian Kernigham who also co-wrote the first C book. You will not really need precise definitions of Ratfor to use it. Statements on a line may be separated by a ”;”. Statements may be grouped together with braces {}. Do loops do not require statement numbers because {} defines the range, etc. The Fortran relational operators ”.gt.,.ge,.ne.,” etc. may be written ”>,⇐,!=,”etc. Unfortunately, the Ratfor switch statement conflicts with “implicit undefined” declaration, consequently we never use it. Ratfor also frees you from FORTRANs strict indentation rules. Anything from a # to the end of the line is a comment. Ratfor offers quite a few more features more and we strongly recommend it to any FORTRAN programmer.